Added composition.addBindingHandler

An experimental helper function that enables the developer to create a
binding handler that will attach itself after the composition.complete
event is fired.
Merge branch 'master' into develop
Change sigma demo to work with new addBindingHandler
Change isotope demo to work with new addBindingHandler
Patch addBindingHandler to clone properties of config object
Merge branch 'feature/addBindingHandler' into develop